Corrosion is an electrochemical process which leads to the deterioration and eventual destruction of exposed metal surfaces. The presence of conducting electrolyte, moisture and oxygen to successfully complete the electrical circuit on the thermodynamically unstable metal surface are the main factors of a corrosion process.
One of the most efficient ways to thwart corrosion is to shield metal surfaces from the environment with protective coatings. These coatings are of great importance for numerous civilian and military uses, including use on ship hulls and topside exterior surfaces, car underbodies, offshore drilling decks, bridges and supports, various fuel, potable water, chemical and sewage tanks, numerous structural and building uses, etc.
Over the years, coatings based on alkyd, urethane, vinyl, acrylic and epoxy paints and other technologies have been developed, and often have included corrosion inhibitor pigments such as zinc, aluminum, zinc oxide, modified zinc oxide and calcium ion-exchanged amorphous silica gel. Using corrosion inhibitor pigments has several disadvantages. Some pigments contain metals that are toxic. Several, including metallic zinc, have high densities and settle. A number of pigments react with resins in the coating. Additional pigmentation also requires added wetting agents that may affect corrosion resistance. Furthermore, such solid corrosion inhibitors require direct application to and contact with the metal surface in order to perform effectively.
Migratory vapor phase corrosion inhibitors have also been developed as additives to coatings to improve the corrosion resistant effect of the coating. These corrosion inhibitors are organic compounds that protect metal surfaces by emitting vapor such as an amine-based compound. The nitrogen on the amine has two electrons that are attracted to the polar metal surface. The corrosion inhibitor migrates to the surface of the metal surface, and when at the surface the rest of the molecule is very hydrophobic and repels water to significantly retard corrosion.
U.S. Pat. No. 4,812,503 describes certain migratory vapor phase corrosion inhibitors, such as amine carboxylates formed by reacting a secondary amine such as dicyclohexylamine with a carboxylic acid, and has shown them to migrate through the paint film following application to a metal surface to form an additional coating where the corrosion inhibitor is in direct contact with the metal surface and further protects the same from corrosion. However, a drawback of the corrosion inhibitor systems described in U.S. Pat. No. 4,812,503 is that the inhibitor is generally dissolved in a hydrocarbon solvent, such as naphtha or mineral spirits, before mixing with the paint and only achieves a concentration of inhibitor in solution of around 5 to 10 weight percent (wt. %). As such, it is necessary to add a large amount of the inhibitor-containing solution to the paint in order to obtain a sufficient concentration of inhibitor in the paint for it to be effective as a metal corrosion inhibitor. Having to add such a large volume of solvent lowers the paint solids content and reduces the dry film coverage per coat to an unacceptable level.